1. Field of the Invention
The present invention relates to a device, a method and a program for detecting a communication frame base point through blind processing. In particular, the present invention relates to a device, a method and a program enabling to detect the base point of a communication frame, to estimate an offset amount from the base point of a communication frame and the like, without a synchronization pattern.
2. Description of Background Art
In a general digital wireless communication system, communication processing is performed by adding a pilot frame, having a synchronization pattern for synchronization processing, to the head of a data frame containing data to be transmitted. If a pilot frame having a synchronization pattern of the communication counterpart is known, it is possible to easily detect the starting base point of the communication frame by sharing the synchronization pattern with each other.
On the other hand, if a pilot frame having a synchronization pattern of the communication counterpart is not known, that is, in a radio wave monitoring system intended for illegal radio wave for example, subject signals are in a wide range, so the synchronization patterns must be provided corresponding to all illegal radio waves, respectively. However, when taking into account a fact the radio wave of the communication counterpart is an illegal radio wave, it is not practical that the radio wave monitoring system reserves countless synchronization patterns in advance.
Further, in an adaptive communication system in which the communication quality is improved by changing the structure of a communication frame corresponding to the quality of a communication path, the communication frame structure for synchronization processing may be changed. Therefore, processing to detect the base point of a communication system and to estimate the offset amount through blind processing is important.
Conventionally, in a processing method for a communication frame of this type, a unique pilot signal is added to a data frame of a communication frame as described above. Further, as a method of detecting a communication frame in a mobile communication system, “Digital Wireless Transmission Technology” by Seiichi Sanpei, Published by Pearson Education Japan (Non-Patent Document 1), Chapter 7 describes that detection of the base point of a communication frame is performed through correlation processing with respect to a known pilot symbol pattern. Referring to Non-Patent Document 1, explanation will be further given by using TDMA (Time Division Multiplexing Access) system as an example.
As obvious from the frame and slot configurations in the 6-channel TDMA system shown in FIGS. 7 and 6 of Non-Patent Document 1, unique words for synchronization processing are added to the head of each channel data, as shown in FIG. 20. In the case of Non-Patent Document 1, the unique words include a carrier phase sync word (CRSW), a symbol timing sync word (STSW), and a slot timing sync word (SLSW). These words have unique data patterns, and are added to each channel individually.
In Non-Patent Document 1, detection processing of frame synchronization is performed such that with respect to a reception database signal 20, correlation between a reception signal and the slot timing sync word which is a known pattern is first calculated by using a correlator 21, as shown in FIG. 21 (FIGS. 7 and 10 of Non-Patent Document 1). If the reception database signal 20 is true frame timing, a correlation peak is caused in the correlation processing by the correlator 21. On the other hand, if the reception database signal 20 is false frame timing, a correlation peak will not be caused in the correlation processing by the correlator 21. That is, processing to detect the base point of a communication frame is performed based on the correlation peak obtained.
Further, in order to prevent performance deterioration due to false correlation peaks, some false correlation peaks are excluded by using a threshold determination device 22. Then, by using a front protection and back protection circuit 23, false correlation peaks caused randomly are removed, and processing of synchronization point of a communication frame is performed.
Detecting a synchronization point of a communication frame by using the unique words mentioned above is same in the case of CDMA (Code Division Multiplexing Access) system.
Next, explanation will be given for a broadcasting system as an example. Broadcast signals are always transmitted continuously. Since the receiving side starts reception at any time, a pilot symbol for synchronization is indispensable in order to know the starting point of a communication frame. Even for the broadcast signals, processing to detect the base point of a communication frame is realized through correlation processing by using known unique words on the receiving side, like the above-described method.
As described above, in the communication processing according to the conventional example, processing to detect the base point of a communication frame is performed such that unique words applied to a subject reception signal are grasped in advance and processed on the receiving side.
In the method of detecting the base point of a communication frame according to the conventional example described above, a synchronization pattern for detecting the base point of a communication frame must be obtained in advance on the receiving side in order to detect the based point of the communication frame. Therefore, it is impossible to apply to a radio wave monitoring device intended for unspecified number of communication waves, and an adaptive communication system in which a communication frames are changed corresponding to the radio wave environment.